This invention relates to a method of applying permanent markings to glass surfaces for purposes of design and identification. The application of permanent markings to glass surfaces is useful for tracing goods, inventorying goods, locating and identifying lost goods and preventing or inhibiting the theft of goods, such as, television sets, automobiles, microwave ovens, furniture with glass components, glass art objects, and the like.
Glass is an amorphous material composed principally of silicon dioxide and alkaline metal oxides. Glass is optionally compounded with other oxides such as boron oxide, lead oxide, zinc oxide, aluminum oxide, alkaline earth metal oxides and the like. Because of glass' chemical makeup and amorphous structure, it is difficult to a permanently mark glass. Conventional means of marking glass comprise engraving, printing or painting, chemical staining and etching. Decals can be placed on glass with the use of a suitable adhesive. However, decals are not permanent markings and can be easily removed by scraping or by dissolving the adhesive with an appropriate solvent. Glass can be engraved with a diamond or carbide tip stylist, engraving tool or the like. Engraving is difficult and requires a skilled artisian to obtain aesthetically acceptable engravings. Engraving has one additional drawback, if the engraving is not done properly, the glass can crack or shatter.
For over a century, it has been known that glass can be etched with hydrogen fluoride. It is believed that the hydrogen fluoride reacts with the silicon dioxide in the glass to form fluosilicic acid and silicon tetrafluoride. There is an equilibrium between fluosilicic acid and silicon tetrafluoride and water. The silicon tetrafluoride, being gaseous, escapes from the glass shifting the equilibrium and causing the fluosilicic acid to decompose into silicon tetrafluoride and water to maintain the chemical equilibrium. The conventional methods of etching glass comprise coating the glass with material resistant to hydrogen fluoride, such as wax or asphaltum, engraving a design in the coating down to the surface of the glass and applying either gaseous hydrogen fluoride or a solution of hydrogen fluoride to the exposed portion of the coated glass surface. The hydrogen fluoride etches the exposed glass surface. The glass surface coated with asphaltum is not etched. After the glass has been etched, the glass is washed and the protective coating is removed by heat treatment, scrapping and/or with an appropriate solvent.
This method of etching glass is extensively used in large scale manufacturing operations employing skilled personnel to engrave or cut out the design in the protective coating and who appreciate the danger of hydrogen fluoride. Normally, the etching takes place in large tanks where the surface of the glass to be etched can be placed in a horizontal or vertical position. This method is not amenable to home use or appliance stores, automobile dealers or art dealers for applying permanent identification marks or other markings to glass articles and articles containing glass components. Use of the above method is limited by (1) the danger and difficulty of handling hydrogen fluoride containing materials; (2) the skill required to engrave or cut out a design in the protective coating on the glass; and (3) the difficulty of applying a hydrogen fluoride-containing composition to a vertical surface, such as an automobile window.
The above difficulties have been recognized for over a century and a number of patents have issued relating to the etching of glass and metals to overcome these difficulties.
U.S. Pat. No. 95,617 teaches a way of eliminating the difficulty in engraving a design in the protective coating. This patent is directed to a process wherein lead letters are laid on top of a glass surface in a horizontal position and the glass is coated with a protective coating around the lead letters. The lead letters are removed exposing the glass surface in the design of the letters. This glass surface is etched by applying a hydrogen fluoride solution.
U.S. Pat. No. 1,832,716 is directed to a method of etching glass which eliminates the step of engraving or cutting out the design in the protective surface. The process comprises applying a sheet of glass over a pattern of the design to be etched on a flat horizontal surface. A protective coating resistant to hydrogen fluoride is applied to the portions of the upper surface of the glass not covering the pattern of the design to be etched. The glass is then sequentially etched in one or more steps to give the final etch design a three dimensional aspect. After the final etching, the glass is washed, the protective coating is removed and the etched side of the glass is given a mirrored coating. U.S. Pat. No. 2,067,925 discloses a paste etching composition for etching glass either by printing or transfer method. The composition contains magnesium carbonate, sugar, catechu or gum senegal, corn starch, semi-refined molasses, water, gum tragacanth, ammonium bifluoride, carbon black and oil of rose geranium.
U.S. Pat. No. 2,127,781 discloses a glass etching process similar to a silk screening operation. The silk screen is coated with an acid resistant material to form a stencil. The silk screen is placed in a silkscreen frame, contacted with the surface of the glass to be etched and a pasty, but not tacky consistency, composition is screened by means of a squeegee or roller through the interstices of the "open" areas of the silkscreen to etch the glass. After the etching is complete, the silkscreen is removed and the glass is washed three times with water. The patent discloses that the etching composition is to be devoid of crystals of ammonium bifluoride. The patent suggests the following etching composition. Seven pounds of ammonium bifluoride and five pounds of cryolite are added to nine pounds of water and the resulting mixture is boiled. The mixture is then allowed to cool to room temperature with stirring. The crystalline free mixture is decanted from any crystals and mixed with one pound of tragacanth gum. The resulting mixture is beat or whipped to form a pasty mass suitable for etching.
U.S. Pat. No. 2,324,694 discloses a method of engraving or cutting out a design in the acid resistant protective coating on a glass surface for preparation for etching. The glass surface is coated on both sides with the protective coating. The glass surface to be etched is then illuminated on the opposite side and an opaque stencil with desired design cut out of the stencil, is interposed between the illumination source and the surface to illuminate the design on the coated surface. The design illuminated on the protective coating is cut out of the protective coating down to the surface of the glass. The exposed glass surface is etched in a conventional manner.
U.S. Pat. No. 3,769,113 discloses a method to deep etch a glass surface. An emulsion of an elastomer is applied to the back side of the glass, that is, the side of the glass that is not to be etched. The elastomer is allowed to dry and then both sides of the glass are coated with a protective coating, such as asphaltum. The side of the glass to be etched is coated with asphaltum in the form of a pattern or a design. The plate is etched in a strong hydrogen fluoride solution with the surface to be etched facing downward to obtain a deep etching action.
U.S. Pat. No. 4,316,766 is directed to a method for applying identification designs on a glass surface. The method comprises forming a stencil from a flexible plastic foil or film perforated by electrostatic means to form a design. Glue or adhesive is applied to back side of the stencil and the stencil is applied to the glass surface to be etched. A paste-like glass etching composition containing ammonium bifluoride is applied to the other side of the stencil to etch the glass and impart the stencil design.
Australian Pat. No. 116,492 (1/21/43) is directed to a bituminous coated stencil for the acid etching of metal surfaces. The stencil comprises a backing sheet onto which is printed or silkscreened a design with a resin not appreciably soluble in a hydrocarbon solvent. Before the resin dries, the resin can be coated with aluminum powder if desired. After the resin has dried, an adhesive soluble in a hydrocarbon solvent is applied to the face of the stencil. The stencil, adhesive face down, is applied to the metal surface to be etched and then the backing sheet is removed leaving the resin stencil on the surface of the metal. The stencil therein is then washed with a solvent to remove the adhesive material not covered by the resin of the stencil. The metal is then etched, washed and the stencil removed to leave an etched design in the metal. In a preferred embodiment, a composition of wax and/or bitumin and/or rosin is applied to the resin side of the stencil. This composition acts as an adhesive material when contacted with a methylated solvent.
British Pat. No. 1,302,796 (1/10/73) is directed to a dry transfer glass etching method. An etching paste is applied to the intaglio areas of an engraved design. Transfer tissue is applied to the engraved design to transfer the paste in the engraved design on to the tissue. The tissue with the paste design is dried. When it is desired to etch glass with the design, the tissue is moistened and applied to a glass surface. Before the moist tissue is applied to the glass surface, a light coating of oil is applied to the glass surface to prevent glass hazing during etching. The etching paste is prepared from ten parts of ammonium bifluoride to one part of a thickening agent with sufficient water to form the paste.